The increasing demands for higher areal recording density impose increasingly greater demands on thin film magnetic recording media in terms of coercivity (Hc); magnetic remanance (Mr); coercivity squareness (S*); medium noise, eg., signal-to-medium noise ratio (SMNR); and narrow track recording performance. It is extremely difficult to produce a magnetic recording medium satisfying such demanding requirements.
The linear recording density can be increased by decreasing the medium noise, as by maintaining very fine magnetically decoupled grains in the magnetic layer of the magnetic medium. Medium noise is a dominant factor restricting increased recording density of high-density magnetic hard disk drives, and is attributed primarily to inhomogeneous grain size and intergranular exchange coupling in the magnetic layer. Accordingly, in order to increase linear density, medium noise must be minimized by suitable microstructure control of the magnetic layer and other layers of the magnetic medium.
The microstructure of the magnetic layer and others layers of the magnetic medium is determined by both the composition of the layers as well as the conditions for reactive sputtering for depositing the layers on the medium. One challenge associated with reactive sputtering is that it is difficult to produce uniform compositions across the substrate surface. Much of the reactive gas is consumed as it passes over reactive surfaces in the sputtering chamber. These surfaces may include the chamber walls, the substrate surface and the substrate holders. Depending on the distribution of material around the substrate surface, the consumption of reactive gases around the substrate can result in non-uniformity of the layers sputtered on the substrate. Due to the close proximity of the substrate holder to the substrate, the holder may have particularly harmful effects on the uniformity of the layer sputtered on the substrate surface.